1. Field of the Invention
The present invention relates to an apparatus generating a seek direction detecting signal for an optical pickup determining the relative position of the center of an optical spot focused on an optical disk with respect to the center of a disk track in a RAM-type optical disk having a land/groove structure, and more particularly, to an apparatus generating a seek direction detecting signal for an optical pickup using a main beam and a sub-beam having a predetermined aberration in the tangential direction of an optical disk.
2. Description of the Related Art
In general, an optical pickup apparatus optically records or reproduces information of an optical disk such as a RAM disk, which is employed as a recording medium for recording/reproducing information. An optical pickup apparatus for this purpose comprises a light source emitting laser light, an objective lens converging light emitted from the light source on an optical disk to form an optical spot on the optical disk, an optical detector receiving light reflected from the optical disk and detecting an information signal and an error signal, and a signal processing portion processing the detected signals.
Referring to FIGS. 1 and 2, a conventional apparatus for generating a seek direction detecting signal for an optical pickup includes a grating (not shown) illuminating a track and adjacent tracks at the same time so as to record/reproduce information, an optical detector, and a signal processing portion.
Referring to FIG. 1, a spiral track having a land (L) and groove (G) structure, is formed on an optical disk 1, and information marks 1a are formed on the land (L) and groove (G). When information is recorded on or reproduced from the optical disk 1, light beams diverged by the grating are focused on the disk 1. That is, a main beam BM is focused on the track recording/reproducing information marks 1a, and first and second sub-beams BS1 and BS2, in which each sub-beam precedes or follows the main beam BM by a predetermined time, are focused on tracks of the optical disk 1 to be ±½ track pitch off the main beam BM in the radial direction of the optical disk 1.
The optical detector includes a main optical detector 2a for receiving the main beam BM reflected from the optical disk 1, and first and second optical sub-detectors 2b and 2c for receiving the first and second sub-beams, respectively. Here, the main optical detector 2a is comprised of two separated plates A and B separated in the radial direction of the optical disk 1 for receiving light independently of each other. In addition, the first and second optical sub-detectors 2b and 2c are comprised of two separated plates C and D, and two separated plates E and F separated in the radial direction of the optical disk 1, respectively.
The signal processing portion is comprised of a plurality of differential amplifiers 3, 4, 5, and 6 for differentiating and amplifying the signals detected by the main optical detector 2a, and the first and second optical sub-detector 2b and 2c to detect a track error signal (TES) and a track cross signal (TCS), a tracking control unit 7 receiving the detected track error signal (TES) and track cross signal (TCS) and outputting a tracking control signal, and an objective lens driving portion 8 actuating an objective lens according to the inputted tracking control signal.
The track error signal (TES) is generated by using a push-pull signal Md output from the main optical detector 2a. The track cross signal (TCS) is generated by using a difference signal S1d-S2d of push-pull signals S1d and S2d output from the first and second optical sub-detectors 2b and 2c, respectively, and the push-pull signal Md. Here, since the first and second sub-beam BS1 and BS2 are disposed ±½ track pitch off the main beam BM, and therefore the push-pull signals S1d and S2d have phase differences of ±90° with respect to the push-pull signal Md, the track cross signal can be detected by using the phase differences.
While the conventional apparatus for generating a seek direction detecting signal for an optical pickup, configured as described above, has an advantage in that the track cross signal can be detected in a relatively simple manner using the three beams, there is a problem in that, since the first and second sub-beams are disposed to precede and follow the main beam BM, cross erasures occur to the adjacent track signals when a RAM-type optical disk is employed.